The present invention relates to a control system, in particular for transport devices as used in aircraft.
Conveyor belts without closed-loop control are generally used for loading aircraft and initially have items of cargo placed on them, across their width, while they are stationary. Typically, once the entire width of the conveyor belt has been completely filled, the conveyor belt is moved onward, so that the load located on the conveyor belt is moved further to the rear into the aircraft.
In loading systems such as these, the loading process is thus broken down into two repeatedly recurring steps, namely a first loading step, in which the load is placed on the belt while it is stationary, and a second conveying step, in which the loaded belt is moved onward. The aircraft can in this way be filled layer by layer by the repeated sequence. Since the total load is increased with each loading step, the load being conveyed also increases in a corresponding manner with each conveying step.
Typically, the first loading steps present no problems for the entire loading process since in this case, firstly, there is still little load to be moved and, secondly, the load is also generally still largely located in the field of view of the load handler. Any sliding of the load, possibly resulting in the conveyor belt being blocked to a greater or lesser extent, can in general still be identified well during these first loading steps. Furthermore, the power of the motor driving the conveyor belt is typically also dimensioned such that, when the conveyor belt is only partially loaded, slight jamming or sliding of the load does not yet actually lead to the conveyor belt becoming totally blocked.
However, it can readily be seen that, as the loading process increases, and the load to be moved as well as the distance of the load from the point where the load is placed on the belt increase, the probability of faults rises, for example due to individual items of cargo sliding or becoming jammed. This can lead to the conveyor belt becoming completely blocked even before it has been completely filled which, particularly in time-critical situations such as when loading and unloading aircraft, can lead to undesirable and possibly costly time delays before the fault is identified and has been rectified. Furthermore, the blocking of individual items of cargo, even when this does not lead to a total blockage, can lead to power surges, which last for greater or lesser times, on the conveyor belt motor, which can in turn shorten the maintenance intervals for the conveyor system, and can reduce its life, in the long term.
While three-phase motors without closed-loop control are generally used at the moment for conveyor belt systems for loading aircraft, FIG. 1 shows a servo drive system with closed-loop control. A regulator 1 receives, as input variables, a nominal rotation speed Nnom and a measured actual rotation speed N. The regulator 1 uses the difference between the actual rotation speed N and the nominal rotation speed Nnom to define a current value Inom which corresponds essentially to a torque level that is to be set. The regulator 1 passes the current value Inom to an amplifier 2, which in turn acts on an actuator (or motor) 3. The actuator 3 operates a load 4. The actual rotation speed N is measured at the actuator 3, and is fed back to the regulator 1.
The servo drive system with closed-loop control shown in FIG. 1, in contrast to the drive system without closed-loop control, allows the torque of the actuator 3 to be readjusted if its rotation speed N does not match the nominal rotation speed Nnom. However, this arrangement has the problem of surges in the load 4, which, if there is a discrepancy between the actual rotation speed N and the nominal rotation speed Nnom, can lead to the power of the actuator 3 being increased, and can thus possibly excessively overload it.
Furthermore, malfunctions, for example due to blocking or jamming of items of cargo, are not identified and can thus further increase the load on the actuator 3.
The present invention is based on the object of providing an improved loading device which can also be used in particular for loading aircraft.
The present invention provides a monitoring unit for monitoring a first control value for overshooting or undershooting of a threshold value, which is used for controlling an apparatus. The monitoring unit in this case has determination means for determining the threshold value from an instantaneous value of the first control value when the apparatus reaches a predetermined operating state. Furthermore, the monitoring unit has monitoring means for monitoring the first control value for overshooting or undershooting of the determined threshold value after the apparatus has reached the predetermined operating state.
By determining the threshold value from the instantaneous value of the first control value when the apparatus reaches the predetermined operating state, the monitoring unit can carry out adaptive monitoring of the first control value, in each case matched to the conditions which also actually occur on reaching the predetermined operating state.
In one preferred embodiment, the determination means has a first identification means for monitoring an operating parameter of the apparatus for identification of the predetermined operating state of the apparatus. The identification means in this case uses the behavior of the operating parameter to deduce that the apparatus has reached the predetermined operating state.
The first identification means preferably has a comparator for comparing a predetermined value of the operating parameter with a modeled value of the operating parameter, in which case, if the values match, it is deduced that the apparatus has reached the predetermined operating state. The modeling of the values for the operating parameter in this case makes it possible to define and vary the reaching of the predetermined operating state irrespective of the actual conditions. This makes it possible, in particular, to reduce the influence of transient processes (for example with an overshoot and/or undershoot), which could incorrectly indicate that the predetermined operating state had been reached.
As an alternative to the model value, the comparator can also compare the predetermined value of the operating parameter with an actual value of the operating parameter. This makes it possible to define the reaching of the predetermined operating state as a function of the actual conditions.
The instantaneous value at the time when the predetermined operating state is reached is preferably stored. This stored value then represents the initial value for further monitoring of the first control value.
In a further embodiment, the determination means has a definition means for defining the threshold value from the instantaneous value of the first control value when the apparatus reaches the predetermined operating state, and from a permissible discrepancy. In this case, the permissible discrepancy may, for example, be a fixed value or may also be adaptively matched to the given conditions.
The monitoring means preferably has a second identification means for identifying whether the first control value is greater than or less than the determined threshold value.
The monitoring means preferably has a third identification means for identifying whether the first control value is greater than or less than the determined threshold value and whether the apparatus is in the predetermined operating state. In this way, the monitoring for overshooting or undershooting of the determined threshold value can be restricted to the time period after the apparatus has reached the predetermined operating state. A warning signal for the apparatus is preferably set when the determined threshold value is overshot or undershot.
The monitoring unit according to the invention is preferably used for a control system, for example for an actuator. The control system can in this case be used in particular for such transport devices, for example those in an aircraft, in which loading initially takes place in a stationary condition and the load is then transported further, as was described initially.